World's First Observation of the Change in Electronic State of Oxygen Associated with Metal-Insulator Transition - A New Viewpoint for Developing Spintronics-Related Materials (Press Release)
- Release Date
- 19 May, 2009
- BL08W (High Energy Inelastic Scattering)
Japan Synchrotron Radiation Research Institute
University of Hyogo
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Japan Synchrotron Radiation Research Institute (JASRI; Akira Kira, Director General) and the University of Hyogo (Nobuaki Kumagai, President), working jointly with Northeastern University (US), Delft University of Technology (Netherlands), and Osaka University, were the first in the world to clarify that not only the electronic state of manganese but also that of oxygen changes when manganese oxide undergoes a transition from its nonconductive state (insulator) into a highly conductive state (metal). This is a result of the combination of high-accuracy experiments on Compton scattering*1 using high-intensity high-energy X-rays produced at SPring-8 and first-principle band theory calculations*2 with high reliability. Manganese oxide, the target in this research, undergoes a characteristic transition from an insulator to a metal when a magnetic field is applied (known as the giant magnetoresistance effect). Nowadays, intensive research is being carried out in developing spintronics*3 technology based on this characteristic. In the past, this giant magnetoresistance effect of manganese oxide has been understood by a model in which only the electronic state of manganese changes. The result of this research, however, clearly indicates the need to consider the electronic state of oxygen. This discovery is expected to bring about a new viewpoint in the basic research into elucidating the mechanism underlying the transition of manganese oxide from an insulator to a metal at the atomic level. It will also greatly contribute to the development of material design for spintronic devices to realize ultrahigh-density memory. This research was carried out by the joint group of Masayoshi Ito, Associate Senior Scientist, and Yoshiharu Sakurai, Associate Chief Scientist at JASRI; Akihisa Koizumi, Associate Professor at the Graduate School of the University of Hyogo; Kazuma Hirota, Professor at Osaka University; and Bernardo Barbiellini, Scientist, and Arun Bansil, Professor at Northeastern University; Peter E. Mijnarends, Professor at Delft University of Technology. The achievement was published online in the American scientific journal Physical Review Letters on 19 May 2009. Publication: |
<Figure>
Fig. 1 Crystal structure of manganese oxide.
Fig. 2 Conventional standard model of metal-insulator transition associated with giant magnetoresistance effect.
Fig. 3 3d electron of manganese and 2p electron of oxygen.
Fig. 4 Anisotropy of electron momentum density distribution (experiment and theory).There is a difference in the anisotropy of the distribution for low pz (<0.7 a.u.) because of the difference between the 2p electronic state of oxygen in ferromagnetic metals and paramagnetic insulators.
Fig. 5 Anisotropy of two-dimensional electron momentum density for ferromagnetic metal obtained from highly reliable and accurate band theory calculation.
Fig. 6 Schematic of Compton scattering.Compton scattering occurs after an elastic collision, such as that between billiard balls, between an electron and an X-ray photon. The momentum (velocity) of an electron before collision can be measured by measuring the energy of the Compton scattered X-ray photon after the collision.
<Glossary>
*1 Compton scattering
This occurs following an elastic collision between an electron and an X-ray photon, similar to a collision between billiard balls (Fig. 6). The momentum (velocity) of an electron before collision can be measured by measuring the energy of the scattered X-ray photon after the collision.
*2 First-principle band theory calculation
A method of determining the electronic state in a crystal only from the principles of quantum mechanics without using experimental data (namely, a first-principle method).
*3 Spintronics
A new technology of reversing the direction of electron spin (the magnetic property of an electron) using electric current or light. Spintronics technology is now being actively developed with the aim of realizing ultrahigh-density memory.
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For more information, please contact: or Dr. Akihisa Koizumi (the University of Hyogo) |
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